This is big news... If you love your Zen amp, and your ears are dialed into it, this will frankly blow you mind. You'll shake your head for at least a year, every time you listen to it. It improves the power, improves the punch, improves the midrange, basically it improves everything.

Well the mod is a success. I've had my Zen for many years now, and it has never ceased to impress how high it's fidelity can get within reasonable means. This tweak has brought this amp to another level, and it's exciting to think that it can be done without raising the cost much. Thanks to Mr Hazen and Mr Deckert for discovering yet another way to make these unassuming amps embarrass expensive gear.

The word 'bloom' keeps coming up in my mind. Dynamics are improved by a large degree. Everything is now more distinct in the separations of instruments in the image, and subtle textures in voices and recording effects. Everything sounds fuller as music surrounds your area with more presence.

It absolutely sounds more pleasant to the ear. The speakers do seem to be disappearing more and a sibilance noticeable on certain albums has smoothed out revealing more details in the mix.

Bass is also more detailed and is finding perfect balance with the rest of the spectrum.

For such a subtle change to the circuit, the effect is really quite surprising. I'm finding it really easy to switch off critical thought and take in the recordings. It's a very inviting presentation.

I have already upgraded to V-Caps, and I would say this is easily as beneficial if not more. Like the V-Caps, it enhances every aspect of the amp without losing any of it's best qualities.

The upgrade is certainly worth the asking price. And considering all those used zen amps out there, offering a lifetime warranty along with the upgrade is a sweet deal.

SteveIn Taboo schematics, I see the the suppressor grid connected to the cathode. Is this internally connected? Because, I see nothing connected to pin 6 inside the amp (pin 6 is the suppressor grid I believe?).

I couldn't agree more, there are no tubes out there, at any cost that are as good as this tweak. I've been using it on the Torri-I for about 3 weeks, and I'm still amazed. I did mine with a switch, so I could have it both ways, the switch was a complete waste of time. This was right after Dennis had done it to Rachel, his integrated, (SE34-I) and Steve wasn't sure it would work, or if I would even like it on the Torri-I. He was so excited about it, which got my curiosity up, I tried it that night. When the switch takes the cap out of the loop, it is almost un-listenable, yet its the same amp as I've always had.

Well I've run low on .1's of the same type in my parts bin, so gotta go get a few more for the old ST70. I WISH it was a Torii II I was modding, but that'll just have to wait til my ship comes in, if it ever does .

Does it make a hoot of a diff if the cap is anything more than of your garden variety generic metallized poly film construction? I think earlier in the thread Steve even said polyester construction (ie mylar) was just fine.

Hey guys, I'm assuming the original SV83 tube applies for the mod (6 & 3 not internally connected). I love this original Svetlana SV83 (6n15nM). If the house was burning and the kids and wife are already safe....I'm going in to get my 6n15nM's.

I have a SE34I.2 with stock rectifiers, Russian Mullard el34 and 6N23P drivers. The speakers used were Decware HDT.I decided to measure the transfer function for power and phase before and after the mod. The signal was taken directly from the output transformer in parallel with the speakers. Only the left channel is shown.

The first graph is for the switch in the position "less bass". Yellow is before the mod, cyan is after.

The second graph is for the switch in the position "more bass". Pink is before the mod, green is after.

Note: the pictures represent the difference between the control and test signals, the absolute value has no meaning here. Only deviation from the straight line matters.The listening experience in general confirms the visual representation. The sound stage became more up-front, did not notice much difference in clarity.

the graphs have been updated. I see almost no static difference before and after the mod. However for both cases the instantaneous dispersion of the transfer function for power and phase was quite substantial (up to 10dB and 240 degrees) during listening especially in the bass region (below 250 Hz). I cannot however imagine how it can contribute to more or less clarity and true dynamics.

No worries, I just mean that I updated the graphs after I removed the resistor. The original graphs were done with the resistor in place.

Instantaneous dispersion is what I see on the live graph when I disable averaging. Both graphs are stable from about 250Hz and up; and below that frequency I can see substantial instantaneous swings both in power (up to 10dB) and phase (up to 240 degrees). The character of those swings might change the perceived spatial information and dynamics rendering(?).

I can hear changes in the sound stage, it became more up-front. In an orchestral recording I did myself the instruments stick out more than I remember in the live feed.

When I have time I will probably measure the amplifier loaded with a resistor instead of the speaker to see if there are any differences. With the HDT load it is only a 40-20000Hz (+-3dB) amplifier with a big phase distortion below 250Hz.

I've used metallized polyprop caps in both my SE84CS and also my old refurbed ST70 (because that's what I had). I used a couple of old "wonder caps" in the SE84CS, and inexpensive xicons in the '70.

The results of this mod, or tweak, is nothing short of astonishing, in my mind. My Select (SE84CS) sounds incredible, as if it had far more power and oomph than before. The whole musicality spectrum went through the roof compared to any other mod or tweek I've experienced. No other tube swapping or signal cap upgrades, et al, had anywhere near the benefit.

The results with my old (but refurbed) Stereo 70 were similarly astounding, as the same mod is possible given EL34 tubes.

I'd personally save the Rusky pio's for another project, and get a couple xicon .1uf's as they're only around a $1 apiece and are relatively small and easy to fit in.

One disadvantage to the Rusky pio's and their large size is this; you'll need to be bending the leads around to situate them, and those thin brittle steel leads can break off as you massage them to fit in place.

Karl

ps- I'll add that the suppressor grid and cathode were already directly hard-wired on my old Stereo 70, and the difference between this and the "CCE" mod was nothing short of astonishing!

Are you saying that on your ST70 the suppressor grid was wired to the cathode, you removed that wire, put a 0.1 uf cap in its place, and noticed a substantial improvement in the sound? Just want to be sure I understand.

for us DIY'ers is this mod listed anywhere step by step whats needed to impliment? I originally thought it was just a cap between pins 3 and 6, today I read a post from Steve that some of the boards used in the zkit1 will need a trace cut and some won't. I don't want to ruin my amp, I don't like the idea of cutting traces on the board as I recall the board is of very good quality, and it's thick with good traces. Is there a way to tell by looking at our board and know if there is extra work to be done? I did a search of the forums and can't find any sort of walk through or list of changes required etc. If anybody with a zkit1 has done this could you please confirm steps needed to complete the mod.

If you can, look under the board and determine where pin 3 and pin 6 of the op tubes are, and then look to see if there is a trace connecting those pins. If there IS a trace connecting them, then that is the trace to be broken.

It's as though there were a wire connecting pin 3 and pin 6 (but here the wire is replaced by the trace) and you wanted to replace that wire with this little .1uf capacitor.

If there is NO trace connecting these pins, then you're free to just solder the cap between pin 3 and pin 6 with no other considerations.

ok we might wanna think about moving this to it's own thread, but, I have board Rev 7 2009, the trace appears to be under the tube socket, and getting the board out of my chassis is not something I even want to think about let alone removing my sockets. I managed to backlight the board and it looks like the trace is a 90 angle from pin 6 to just below the silk screen 3 for pin 3 with a little leg to pin 3. Could I drill through the board right where the 3 is silk screened and cut the trace that way? This won't hurt anything else will it? I'm thinking Steve is going to have to answer this.

I also have board rev7 2009, and my impression was that pin 6 was unconnected. However my board is installed and I do not have a photograph of the tube-holder side before the holders were installed.

Will check this out today, because I now see that it is possible that my caps are shorted out by the leg of the trace under the tube holders.

UPDATE - GOOD NEWS and BAD NEWS

Well - dug out the multimeter, and it turns out that my CCE caps are indeed shorted out on the tube-side of the board. A pain now to try and cut that trace - but better sound quality to come in the end!

Can somebody please publish a photograph of the tube side of the board showing how these traces run. Steve - could you please indicate which revision of the boards first incorporated the pins 3-6 traces.

yeah I was thinking of a dremel tool with a very small bit to go through from the exposed side of my board.

Alan, if you get it done before me let us know how it goes, I'm going to try to get mine done this weekend, I just need a pack of fine bits. I'll report back when I get mine complete. I'd still like to hear from Steve that there isn't something else in this area I'm going to cut through that I need to worry about.

Sitting looking at the internals right now - got a Dremel not too far away, but I currently have no idea exactly how these traces run on the non-silk-screened side. Obviously, even if I could get the board out, tube holders cannot be removed, and there is little clearance in which to work.

Will let you know what I do - having read this thread, it is not really an option to leave it without the mod!!

UPDATE

Using a dentist's mirror to redirect a strong light behind the board, I can see through the PCB and make out the traces. It runs from 6, across to 3, then out of the tube holder and across to join the other pin 3. Looks to me like the hole should be drilled roughly between the numbers 5 and 6 in order to cut just the 3-6 trace, but leaving pin 3 connected to the trace running out of the tube holder.

Happy to mark out and drill on the basis of the light shining through the board - but I'm not doing ANYTHING till all this is confirmed.